1. Technical Field
This invention relates generally to machining equipment, and more particularly to a collet adapter for adapting a collet to a mounting fixture having a bore with a bore forward bore entrance smaller than the head of the collet.
2. Description of Related Art
A collet is a workpiece-holding component that includes a collet head and a collet body. The collet head has multiple, circumferentially spaced, workpiece-gripping segments. The collet body fits into a collet-holding mounting fixture (herein called a xe2x80x9cbullnosexe2x80x9d) that is bolted onto the rotatable spindle of a lathe or other unit of machining equipment. The combination of the bullnose and the collet is sometimes called a collet chuck.
The bullnose defines a bullnose bore into which the collet body fits, and a tapered bullnose bore wall at a tapered forward entrance to the bullnose bore that provides a bullnose cam surface facing the collet. After inserting the collet body into the bullnose bore and coupling the inward end of the collet body to a hydraulically powered, axially movable, activating linkage on the unit of machining equipment (sometimes called a xe2x80x9cdraw tubexe2x80x9d), the machinist actuates the draw tube to further advance the collet body axially into the bullnose bore. As that occurs, a frusto-conically shaped circumference of the collet head (i.e., a collet cam surface) bears against the tapered bullnose bore wall (i.e., the bullnose cam surface). The resulting cam action closes the collet head against the workpiece, thereby to hold and rotate the workpiece for machining purposes.
Although this type of collet chuck works well in many instances, certain problems arise with a larger workpiece. In some cases, the workpiece is sufficiently large that the collet head is bigger than the entrance to the bullnose bore. So the collet is provided with a collet cam surface in the form of a frusto-conically shaped collet neck intermediate the collet head and the collet body. The tapered bullnose bore wall bears against the collet neck to close the collet head, instead of bearing against the circumference of the head. As a result, a lesser component of force is transmitted to the collet head and so the collet head does not close as tightly against the workpiece as the machinist may desire for a firm hold.
Of course, the machinist can maintain a set of bullnose components with different size bores. But that is an expensive alternative. Also, it involves the time and inconvenience of changing the bullnose. Thus, machinists need a better way to use a bullnose with a collet having a head larger than the entrance to the bullnose bore.
In line with the above, it is an object of this invention to overcome the foregoing and other disadvantages of prior art collet chucks. This object is achieved by providing a collet adapter for a collet having a collet head larger than the entrance to the bullnose bore. The collet adapter includes a hollow sleeve portion that fits into the bullnose bore and a collet-head-receiving portion that occupies a position ahead of the bore. A cam surface on the collet-head-receiving portion mates with the frusto-conically shaped circumference of a particular collet head for purposes of bearing against the collet head to close the collet. The machinist simply uses the collet adapter when the size of the workpiece dictates use of the larger collet head. A set of different size collet adapters enables use of just one bullnose for various collet head sizes.
To paraphrase some of the more precise language appearing in the claims, an adapter constructed according to the invention includes a collet-receiving component disposed symmetrically about an adapter rotational axis. It includes a collet-head-receiving portion and a sleeve portion, and it defines an adapter bore having a size that mates with the collet body so that the collet body fits coaxially into the adapter bore. The collet-head-receiving portion defines a collet-head-receiving space having a size and shape that mate with the collet head so that the collet head fits coaxially into the collet-head-receiving space for purposes of enabling the collet-head-receiving portion to close the collet head against a workpiece. The sleeve portion is centered on the adapter rotational axis and extends axially from the collet-head-receiving portion. It mates with the bullnose bore so that the sleeve portion fits coaxially into the bullnose bore. It functions as means for mounting the collet-receiving component on the bullnose in an operative position such that the collet-head-receiving portion is disposed ahead of the forward face of the bullnose and the bullnose rotational axis and the adapter rotational axis coincide.
A collet adapter assembly constructed according to the invention includes the adapter, a collet, and an adapter-nut-and-machine-screw combination for coupling the collet body to the draw tube on a unit of machining equipment. A mounting fixture constructed according to the invention includes at least two screw holes in its forward end for use in screwing a collet-head-receiving component onto the forward face of the mounting fixture.
Thus, the invention significantly facilitates use of a bullnose mounting fixture with a collet having a collet head larger than the forward entrance to the bullnose bore. The following illustrative drawings and detailed description make the foregoing and other objects, features, and advantages of the invention more apparent.